This invention relates generally to magnetic data storage systems, more particularly to magnetoresistive read heads, and most particularly to structures incorporating an insulating barrier, as well as methods for making the same.
Magnetic disk drives are used to store and retrieve data for digital electronic apparatuses such as computers. In FIGS. 1A and 1B, a magnetic disk data storage system 10 of the prior art includes a sealed enclosure 12, a disk drive motor 14, and a magnetic disk, or media, 16 supported for rotation by a drive spindle S1 of motor 14. Also included are an actuator 18 and an arm 20 attached to an actuator spindle S2 of actuator 18. A suspension 22 is coupled at one end to the arm 20, and at its other end to a read/write head or transducer 24. The transducer 24 typically includes an inductive write element with a sensor read element (which will be described in greater detail with reference to FIG. 2). As the motor 14 rotates the magnetic disk 16, as indicated by the arrow R, an air bearing is formed under the transducer 24 causing it to lift slightly off of the surface of the magnetic disk 16, or, as it is termed in the art, to "fly" above the magnetic disk 16. Alternatively, some transducers, known as "contact heads," ride on the disk surface. Data bits can be read along a magnetic "track" as the magnetic disk 16 rotates. Also, information from various tracks can be read from the magnetic disk 16 as the actuator 18 causes the transducer 24 to pivot in an arc as indicated by the arrows P. The design and manufacture of magnetic disk data storage systems is well known to those skilled in the art.
FIG. 2A depicts a magnetic read/write head 24 including a write element 28 and a read element 26. The edges of the write element 28 and read element 26 also define an air bearing surface ABS, in a plane 29, which can face the surface of the magnetic disk 16 of FIGS. 1A and 1B.
The write element 28 is typically an inductive write element. A write gap 30 is formed between an intermediate layer 31, which functions as a first pole, and a second pole 32. Also included in write element 28, is a conductive coil 33 that is positioned within a dielectric medium 34. As is well known to those skilled in the art, these elements operate to magnetically write data on a magnetic medium such as a magnetic disk 16.
The read element 26 includes a first shield 36, the intermediate layer 31, which functions as a second shield, and a read sensor 40 that is located between the first shield 36 and the second shield 31. A common type of read sensor 40 used in the read/write head 24 is a magnetoresistive (MR) sensor. A MR sensor (e.g., AMR or GMR) is used to detect magnetic field signals by means of a changing resistance in the read sensor. When there is relative motion between the MR sensor and a magnetic medium (such as a disk surface), a magnetic field from the medium can cause a change in the direction of magnetization in the read sensor, thereby causing a corresponding change in resistance of the read element. The change in resistance can then be detected to recover the recorded data on the magnetic medium.
While some read sensors operate in current-in-plane (CIP) mode, others operate in current-perpendicular-to-plane (CPP) mode. FIG. 2B is a perspective view of a read sensor 40 that operates in CPP mode. A bottom lead 42 is in electrical contact with a bottom layer 44 of the read sensor 40, while a top lead 48 is in electrical contact with a top layer 46 of the read sensor 40. While the top and bottom leads 48, 42 are shown electrically insulated from the second and first shields 31, 36, respectively, they can alternatively be coincident, with the shields operating as leads.
A sensing current I is passed between the top and bottom leads 48, 42, and therefore passes substantially perpendicular through the read sensor layers 50, including the top and bottom layers 46, 44. As with other MR read sensors, this sensing current is used in conjunction with changing resistance of the read sensor to detect data from nearby magnetic media. Various read sensors can be used in the CPP mode, with various layers and their combinations. For example, a spin valve read sensor can be used, various configurations and formations of which are known to those skilled in the art.
Increasing read performance is a function of increase of the signal .DELTA.V that can be detected across the read sensor 40. In turn, the signal .DELTA.V detected from operation of the read sensor is a function of the sensing current I that is passed through the read sensor, and the sensor resistance change .DELTA.Rs during operation. More particularly, as is well know in the art, the signal .DELTA.V is essentially equal to the product of the sensing current I and the sensor resistance change .DELTA.Rs.
Spin valve sensors rely on the magneto tunneling effect, which is believed to be a result of the asymmetry in the density of states of the majority and minority energy bands in a ferromagnetic material. Thus, the sensor resistance, which is inversely proportional to the spin-polarized tunneling probability, depends on the relative magnetization orientations of the two electrodes on either side of an insulating barrier layer. In the parallel orientation there is a maximum match between the number of occupied states in one electrode and available states in the other. In the antiparallel configuration the tunneling is between the majority states in one electrode and minority states in the other. W. J. Gallagher, S. S. Parkin et al., J Appl. Phys. 81 (8) April 1997, p.3741-6.
To maximize the effectiveness of such an insulating barrier layer it is desirable to minimize any defects that could create shorting through the layer, which would render it substantially ineffective. The thickness T of the insulating barrier, measured along the current path, is also desired to be minimized while maintaining a barrier. It is also desirable to maintain a band gap on the order of about 1 eV to about 10 eV, where the band gap is a measure of the separation between the energy of the lowest conduction band and the highest valence band. Further, it is desirable to maximize the smoothness of the surface of the insulating barrier on which a succeeding layer is to be formed.
In the past, read sensor designs have included insulating barriers formed of alumina. Alumina insulating barriers can be formed by known methods, including deposition of aluminum metal by physical vapor deposition, evaporation, or ion beam deposition, for example. After such deposition, the aluminum can then be oxidized in O.sub.2 plasma. Such processes can result in an alumina layer having a thickness T in the range of about 10 .ANG. to about 50 .ANG., and a band gap in the range of about 1 eV to about 5 eV. While such thicknesses and band gap values may be adequate, unfortunately these processes and materials result in significant defects, and therefore significant probability of shorting.
Alumina and other materials formed by reactive sputtering can alternatively be used to form an insulating barrier. For example, hafnium oxide (HfO.sub.2), zirconium oxide (ZrO.sub.2), or tantalum oxide (Ta.sub.2 O.sub.5) can be formed by reactively sputtering from a metallic target using an RF or DC magnetron. However, while these oxides may be able to exhibit satisfactory band gap values and thicknesses, they still may be likely to include defects that may result in shorting. Further, each of these materials can be adversely affected by techniques that may be used in later processing operations of the read element, read/write head, or slider. For example, these materials may be soluble in one or more of the developers or strippers used in conjunction with photoresistive materials used during fabrication. Agents such as fluorine or chlorine would need to be used in the RIE processing, however these may cause undesirable corrosion of other device elements. Of course, physical sputtering with ion beam etching could be used instead of RIE, however this might not lend the same degree of selectivity, as is known by those of ordinary skill in the art.
In a particular read sensor design it also may be desired to maintain a particular maximum limit of a shield-to-shield spacing STS1 between the first and second shields 36 and 31. In particular, this is desired to reduce the pulse width for facilitating higher data density reading. Thus, minimizing the thickness T of the insulation barrier can facilitate maintaining the shield-to-shield spacing STS1, and may add flexibility to thicknesses of other layers.
Thus, what is desired is a read sensor that includes an insulation barrier that is more defect free than the insulation barriers of the prior art, while maintaining at least comparable band gap values and thicknesses. Further it is desired that such an insulation barrier be more robust with respect to typical fabrication processes, without involving substantially greater cost or complexity.